This Week in Science

Science  07 Jun 2013:
Vol. 340, Issue 6137, pp. 1139
  1. From Dust Grains to Planets

    Almost 900 extrasolar planets have been identified, but we still struggle to understand exactly how planets form. Using data from the Atacama Large Millimeter Array, van der Marel et al. (p. 1199; see the Perspective by Armitage) report a highly asymmetric distribution of millimeter-sized grains surrounding a young star. Modeling suggests that these particles—the material from which planets form—are being trapped within a protoplanetary disk by an anticyclonic vortex. Localized concentration of large grains within a protoplanetary disk is thought to be a step in planet formation.

  2. Trapped and Coupled

    Trapped single atoms are ideal for storing and manipulating quantum information. Thompson et al. (p. 1202, published online 25 April; see the Perspective by Keller) were able to control single atoms interacting coherently with a field mode of a photonic crystal cavity. An optical tweezer was used to trap the single atom, which enabled positioning of the atom in close proximity to the photonic crystal waveguide, coupling the atom to the optical mode of the cavity. Such coupling should prove useful in quantum measurement, sensing, and information processing.

  3. A Comet in the Sun


    In 2011, comet Lovejoy plunged into the solar atmosphere and survived its flight through a region of the Sun that has never been visited by spacecraft. Downs et al. (p. 1196) used spacecraft observations of this Sun-grazing comet, combined with advanced magnetohydrodynamic simulations, to constrain the magnetic field of the solar atmosphere—a quantity that has been very difficult to measure directly.

  4. Sonic Boom from Below

    Seismic shear waves released by an earthquake typically far outpace motion along the fault surface. Occasionally, however, earthquakes along strike-slip faults appear to propagate so that the rupture velocity is faster than shear waves, creating a sort of sonic boom along the fault surface. Passelègue et al. (p. 1208) were able to reproduce and measure these so-called supershear ruptures in stick-slip experiments with two pieces of granite under high applied normal stress. Much like during a sonic boom when a plane travels faster than the speed of sound, the ruptures created a shock wave in the form of a Mach cone around the rupture front.

  5. Essential Novelty

    The evolution of essential function for newly originated genes presents a conundrum, in that prior to the gene's origin either the essential function was absent or else performed by another gene or set of genes. In order to better understand how new genes acquire essential function, Ross et al. (p. 1211) investigated the origin of the Drosophila gene Umbrea. Umbrea became an essential protein in certain Drosophila species through the gain of localization at the centromere and a role in chromosome segregation.

  6. Tolerance Needed

    It's a common enough occurrence: You're sick as a dog with a cold, but the person in the office next door just has a few sniffles. What accounts for this difference? Most commonly, these sorts of differences are chalked up to differences in resistance—perhaps you have higher viral loads than your office mate. But such differences can also involve differences in the ability to tolerate the same amount of virus. Deciphering the contribution of resistance versus tolerance, however, is difficult. Jamieson et al. (p. 1230, published online 25 April) studied a mouse model of viral and bacterial co-infection where tolerance and resistance could be separated. Mice infected with influenza virus were more likely to succumb to a secondary infection with Legionella pneumophila as a result of impaired tolerance to tissue damage, rather than because of a difference in bacterial burden.

  7. What Causes Obsessive Compulsive Disorder?

    Obsessive compulsive disorder is a severe, chronic mental illness that affects millions of individuals. However, the mechanisms underlying this disease are still largely unknown (see the Perspective by Rauch and Carlezon Jr.). Ahmari et al. (p. 1234) stimulated glutamatergic pathways between the orbitofrontal cortex and the ventromedial striatum and used grooming to assess obsessive compulsive behavior in mice. Repetitive stimulation over days triggered changes in the neuronal responses of the ventromedial striatum. Over time, the behavior of the animals became independent of stimulation and could be prevented by the antidepressant fluoxetine. Burguière et al. (p. 1243) investigated the neural basis of obsessive compulsive symptoms in a mutant mouse that showed excessive expression of a conditioned form of grooming.

  8. Thank Your Mother


    Maternal effects and influence can sometimes prepare unborn offspring for some of the environmental conditions they may face. Dantzer et al. (p. 1215, published online 18 April) monitored a population of red squirrels and found that both natural and artificially induced increases in the number of conspecific calls increased the growth rate of pups because of increased glucocorticoid levels in the mother. The density stress experienced by mothers thus appears to stimulate them to produce pups that will grow faster and hopefully outcompete the many other pups expected to be produced in the dense population.

  9. Collinearity Cracked in Tetrapod Limbs


    During limb development, the time a nd place of Hox transcription are fixed by respective gene position within the gene cluster. Andrey et al. (p. 1234167; see the Perspective by Rodrigues and Tabin) found that this enigmatic property results from the opposite and successive actions of two large regulatory landscapes located on either side of the mouse Hox locus. In the early phase, one of these topological domains regulates transcription in the proximal limb until a switch occurs toward the other topological domain, which takes over the regulation in the distally developing digits. As a side effect of this antagonistic regulatory strategy, cells in-between have lessened Hox transcription, which generates the wrist.

  10. Unraveling Entanglement

    Entanglement is a curious property of some quantum mechanical systems, exploited in applications such as quantum information processing. Walter et al. (p. 1205) used an algebraic geometry approach to represent the entanglement of a multiparticle system in a pure state in the geometric space whose axes are associated with the properties of the individual particles. In that space, entanglement classes—collections of entangled states that can be transformed into each other—correspond to different convex polytopes, making it possible to distinguish between the classes.

  11. Lock and Load in the Cold

    Muscle extensibility can act as an energy storage vehicle, like springs bouncing back after being compressed. George et al. (p. 1217, published online 25 April) now show that energy can also be stored within muscles as a function of their natural temperature gradient. In hawkmoth muscle myofilaments, reduced cross-bridge cycling regionally constrains myofilaments, resulting in a "lock-spring lattice" that enables elastic energy storage as both the myofilaments and cross-bridges deform. Elastic energy stored in cross-bridges that remain bound and elastically deformed at the end of the first half of a contraction cycle can be released during the second half, thus serving as an additional elastic force. Such "bonus" energy may be especially important given the high energetic demands of flight, but because temperature gradients are a natural result of energy generation and heat dissipation in muscle, this mechanism could be more broadly important in locomotion systems.

  12. Sending Out an ROS

    The global imprint of biological activity in aquatic environments is often considered a consequence of enzyme-mediated redox reactions that support metabolic activity, such as reducing oxygen during respiration. But some organisms also release redox-active reactive oxygen species (ROS) into the environment—to acquire trace metals or to prevent viral infections—which can influence global processes like nutrient availability and contaminant transport. Photosynthetic organisms like phytoplankton are thought to be the primary biological source of ROS in freshwater and marine environments. However, Diaz et al. (p. 1223, published online 2 May; see the Perspective by Shaked and Rose) now show that a broad range of ecologically and phylogenetically diverse heterotrophic bacteria also produce large quantities of superoxide. Production rates vary widely across 30 common bacterial isolates but in some cases were greater than production rates of phytoplankton. Because these bacteria do not require light to grow, they may be the dominant source of ROS in dark environments like the deep ocean, terrestrial soils, or lake sediments.

  13. Improve the System

    A "systems biology" approach may clarify, for example, how particular proteins determine sensitivity of bacteria to extremes of temperature. Chang et al. (p. 1220) integrated information on protein structure with a model of metabolism, thus associating the protein structure of enzymes with their catalyzed metabolic reactions. The effects of temperature on susceptible proteins could be predicted and the key reactions that were likely to mediate sensitivity of bacteria to extremes of temperature were identified. Indeed, engineered thermotolerant proteins could be substituted for sensitive ones to improve the growth of thermosensitive strains of bacteria. Such control could come in handy when engineering strains of bacteria to produce compounds of industrial or therapeutic value.

  14. Getting Active

    The P450 cytochromes are a family of enzymes that contain a heme cofactor and catalyze the oxidation of organic substrates, including drugs. Protein partners are required to deliver electrons to P450. Insight into this mechanism has come from studies of bacterial P450cam; however, a lack of structures of redox complexes has hindered understanding. Tripathi et al. (p. 1227) describe the high resolution crystal structures of oxidized and reduced P450cam complexed with its redox partner putidaredoxin (Pdx). Pdx favors binding to the more open form of P450cam, which enables establishment of the water-mediated H-bonded network required for proton-coupled electron transfer and O2 activation.

  15. Dividing the Brain

    The cerebral cortex of the brain is organized into primary cortical areas, which receive direct inputs from the thalamus, and higher-order cortical areas, which in turn receive inputs from one or more primary cortical areas. Chou et al. (p. 1239) investigated the mechanisms underlying the specification of higher-order cortical areas. Input from the dorsal lateral geniculate nucleus into the primary visual area (V1) is required to drive the genetic and functional differentiation of a large visual cortical field into primary and higher-order visual areas. Thalamocortical axon input acts on a large visual cortical field. The afferents from the dorsal lateral geniculate are necessary to further refine the cortex into subareas that distinguish V1 from higher processing areas. In the relatively simple model that emerges from these findings, sensory input is essential to distinguish primary and higher-order cortical areas.

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